Control system for hydraulic extrusion press

ABSTRACT

A computer control system for hydraulic extrusion presses and the like characterized in that the operator need only preset at a control console certain lengths and distances dictated by the characteristics of the billet to be extruded, without the necessity for setting limit switches on the press itself. Aside from this, the operation of the press is automatic during an extrusion cycle, resulting in smoother operation of the press, improvements in yield and greater uniformity of product. In addition, the control system incorporates an automatic slowdown of the stem before it contacts a dummy block and billet, thereby reducing damage to dies.

United States Patent Johnes et a1.

[54] CONTROL SYSTEM FOR HYDRAULIC EXTRUSION PRESS Allegheny LudlumIndustries, Breckenridge, Pa.

Filed: Nov. 9, 1970 Appl. No.: 87,903

[73] Assignee: Inc.,

U.S.Cl.,

Int. Cl. Field of Search ..235/l5l.l, 72/21, 72/253 ..G06g 7/48, B21623/00 ..235/15l.1, 151; 72/21, 22, 72/8, 253, 347, 453, 26

[56] References Cited UNITED STATES PATENTS 3,043,425 7/1962 Grohmannetal. ..72/22 PUMP / CONTROL Mar. 14, 1972 Primary Examiner.loseph F.Ruggiero Attorney-Brown, Murray, Flick & Peckham [5 7] ABSTRACT Acomputer control system for hydraulic extrusion presses and the likecharacterized in that the operator need only preset at a control consolecertain lengths and distances dictated by the characteristics of thebillet to be extruded, without the necessity for setting limit switcheson the press itself. Aside from this, the operation of the press isautomatic during an extrusion cycle, resulting in smoother operation ofthe press, improvements in yield and greater uniformity of product. Inaddition, the control system incorporates an automatic slowdown of thestem before it contacts a dummy block and billet, thereby reducingdamage to dies.

5 Claims, 1 Drawing Figure UP-DOW/V COUNTER COMP/1 RA 70/? COMPARATORCALCULATE LS/Z L572 CP- .SFDA

CONTROL SYSTEM FOR HYDRAULIC EXTRUSION PRESS BACKGROUND OF THE INVENTIONIn the usual extrusion press installation, a heated metal billet isinserted into a billet container having a die at one end, thearrangement being such that a billet is forced through the die by meansof an extrusion stem which enters the end of the container opposite thedie. Usually, a so-called dummy block is inserted between the billet andthe stem.

Most prior art extrusion presses of this type are controlled by anoperator who initiates an extrusion cycle, whereupon the stem movesforwardly under low hydraulic pressure at a high advance speed until thestem enters the billet container and forces the billet against the die.Since the billet can no longer move freely once the die is contacted,the low hydraulic pressure rises and changes the stem hydraulic systemfrom a low to a high extrusion pressure. Now the stem moves forwardlyunder high pressure into the billet container, causing the billet to beextruded through the die at whatever speed the available pressure willextrude the material of which the billet consists. During actualextrusion, the press operator may exercise a limited degree of controlover the stem speed by manipulation of a lever which, throughappropriate electrical circuitry and mechanical devices, regulates thehydraulic system. The forward motion of the stem is usually stopped by alimit switch mounted on the press which is set to allow for apredetermined thickness of discard.

While press control systems of the type described above are generallysatisfactory for slow speed presses, they have certain deficiencies athigh speeds. Firstly, the press is rough and noisy in its operation. Thestem contacts the billet at rapid advance speed, causing the billet tostrike the die or die holder at this rapid speed which may injure thedie or the ceramic coating of the die in the case of a Sejoumet-typeextrusion press. The stem speed may, and usually does, vary widely notonly during any single extrusion stroke but also from cycle to cycle,thus affecting the uniformity of the product. Also, since the systemuses limit switches these must be relocated at times, an operation whichrequires skill and precision and which is time consuming. Finally, theuse of a limit switch to stop the stem at the end of its stroke does notfacilitate easy adjustment of the discard length of the billet remainingin the billet holder, a factor which tends to reduce yield.

SUMMARY OF THE INVENTION In accordance with the present invention, acontrol system for an extrusion press is provided in which the positionof the stem with respect to an extrusion die is monitored by means of apulse generator which generates a number of pulses proportional to thetravel of the stem from its stationary, fully retracted position. Theoperator initially enters into the control system by thumbwheel switchesor the like the length of the press tool stack, the length of the stemand the dummy block length. In many cases, these will remain constantfrom billet to billet but may vary for each billet as in the case wherespecial metals, such as titanium,.are being extruded on ajobshop basis.Additionally, the operator enters the length of the billet beingextruded, the desired discard length, the desired slowdown distance ofthe stem from fast advance and the desired slowdown distance of the stemfrom extrusion speed. From these quantities, and taking into account thetotal distance between the stem in its fully retracted position and theend of the tool stack, the position of the stem for slowdown from fastadvance, for slowdown from extrude speed,

and the desired final position of the stem can be calculated andutilized to control the press.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying single figure drawing which schematicallyillustrates one embodiment of the invention.

With reference now to the drawing, one type of extrusion pressinstallation is schematically illustrated and includes a main,stationary crosshead 10 which carries a main power cylinder 12 and tworapid advance and pullback cylinders 14 and 16. Reciprocable within themain power cylinder 12 is a ram-type piston 18 connected at its forwardend to a reciprocable main crosshead 20 which can travel back and forthon guideways, not shown. The cylinders 14 and 16 have pistons 21 thereinwhich are connected through piston rods 22 to the main crosshead 20 oneither side of the ram-type piston 18. The main crosshead 20, in turn,carries a stem 24 on its forward face. In the embodiment shown herein,the stem is hollow and receives a piercer ram 26. The ram 26 is utilizedin the case of hollow extrusions and extends through a bore in a billet.Separate hydraulic cylinders, not shown, are provided for causing thepiercer ram 26 to extend out beyond the end of the stem 24.

At the end of the press opposite the main crosshead 20 is a billetcontainer 28 provided with an internal bore 30 having at its one end adie 32 which is backed up by a tool stack or tool block 34 which, inturn, engages a tail block 36 secured to the press foundation.

Hydraulic fluid for actuating the cylinders 12, 14 and 16 is suppliedfrom a reservoir 42. The fluid from the reservoir 42 is pumped by meansof a pump 44, driven by motor 45, to one of two hydraulic conduits 46 or48. The motor 45 continually rotates in one direction; while the pump 44is preferably of the reversible, variable volume type controlledmechanically by a pump control unit 64 to cause fluid under variablepressure to flow from either one of the two pump output ports. When thecondition of the pump 44 is such as to pressurize conduit 46, thepistons 21 within cylinders 14 and 16 are caused to move to the right asviewed in the drawing. This causes the main crosshead 20 to move to theright also, thereby pulling the ram-type piston 18 to the right. Duringthis time, a dumping valve 50 permits liquid from the reservoir 42,which is usually located above the cylinder 12, to flow by gravity intothe left end of the cylinder 12 vacated by the advancing piston 18 whichis moving to the right. Thus, as the crosshead 20 and ram-type piston 18move to the right, the space behind the piston 18 is filled with liquid.

In the operation of the press shown in the drawing, the billet 38 isinitially inserted into the bore 30 in billet holder 28 along with thedummy block 40. This is accomplished by a billet loader, part of anyextrusion press, not shown herein. Thereafter, the pump 44 is activatedto pressurize conduit 46, thereby forcing pistons 21 in cylinders 14 tothe right, causing the crosshead 20, the stem 24 and the ram-type piston18 to move to the right. During this time, the space within the cylinder12 being vacated by the piston 18 is constantly being filled with liquidfrom reservoir 42 as explained above.

In the prior art operation of a press of this type, the rightwardmovement of the stem 24 continues until its forward end is within thebore 30 and forces the billet 38 against the die 32. At this point, thepressure within conduit 46 rises, thereby causing the dumping valve 50to disconnect the cylinder 12 from the reservoir 42 and connect it tothe conduit 46, whereby fluid under pressure is admitted into the leftend of the cylinder 12. This causes the piston 18, the crosshead 20 andthe stem 24 to move forwardly into the billet container 28 at reducedspeed while exerting a higher pressure, whereby the billet is extrudedthrough the die 32. The forward movement of the stem 24 continues untilthe billet is almost completely extruded; however a certain discardlength, identified by the letter D in the drawing, is not extruded toavoid the possibility of jamming the dummy block 40 against the die 32and damaging the same. The cross-sectional area of piston 18 is muchgreater than the combined areas of pistons 21 such that when the systemswitches from rapid advance to extrude, the stem slows down, but thepressure it exerts is much greater.

After the billet is extruded up to the point where only the discardlength remains, the billet container 28 is moved away from the die 32 bymeans, not shown; whereupon the extrusion is severed and the remaininglength of the billet (i.e., the discard length) and the dummy block 40are pushed out of the right end of the bore 30. At this point, fluidflow through the pump 44 is reversed; conduit 48 is pressurized, and thecylinders l4 and 16 caused to return the crosshead 20, the piston 18 andthe stem 24 to the left back into their fully retracted positions shownin the drawing. During this time, the dumping valve 50 permits fluidfrom the left end of cylinder 12 to be returned back to the reservoir42.

As was explained above, in prior art systems the billet contacts the diewith the stem 24 traveling at relatively high speed which sometimesresults in damage to the die. Furthermore, the system requires the useof a limit switch to stop the movement of the stem 24 at its extremelimit of travel. This limit switch is engaged by the crosshead 20 or byan element connected thereto and movable therewith. Positioning thelimit switch, in turn, is time consuming and requires a certain amountof skill. Finally, since the speed of the stem 24 during an extrusionprocess was under the control of an operator in accordance with priorart systems, the quality (e.g., density) of the resulting extrusion wasnot altogether uniform.

In accordance with the present invention, a computer control system isprovided wherein the position of the stem 24 with respect to the die 32is constantly monitored by means of a pulse generator 51 connected to agear 52 which engages a rack 54 carried on the main crosshead 20. Itwill be appreciated, however, that other and different systems can beutilized to generate a number of pulses indicative of the travel of thestem 24 from its completely retracted position.

The control system for the extrusion press includes an operators console55 which, among other things, includes a plurality of thumbwheelswitches which feed digital signals into a computer, generally indicatedby the reference numeral 56, proportional to certain predeterminedlengths. The operator inputs include the length of tool stack 34 (TS),the length of billet 38 (B) and the length of stem 24 (S). Each of theseis entered on a four-decade thumbwheel switch, not shown, which stops at39.99 inches maximum. In addition, the opera tor enters the length ofthe dummy block 40 (DB), the discard length (D), the slowdown distancefrom fast advance (SDFA) and the slowdown distance from extrude speed(SDES). Each of these is entered on a three-decade thumbwheel switch,not shown, which stops at 9.99 inches maximum. The slowdown distancefrom fast advance (SDFA) is that distance which the stem 24 travels atreduced speed with cylinders 14 and 16 being pressurized until the stemforces the billet 38 into engagement with the die 32. This slowdown, asexplained above, is for the purpose of preventing damage to the die. Theslowdown distance from extrude speed (SDES) is that distance which thestem should travel at the end of an extrusion step at reduced speed. Thecomputer 56 utilizes the information entered by the operator to find thedistances from the zero reference (i.e., the fully retracted position ofstem 24) to the following points on the press:

(LS l 2) slowdown from fast advance, (LS7A) slowdown from extrude speed,and (LS7) stop.

The computer 56 is preferably a general purpose computer which may beprogrammed in accordance with techniques well known to those skilled inthe art; however it will be described herein as if it constitutedhardward logic. The first step in the process, which may be performed ina digital subtracter 58, is to determine the quantity AL which is anintermediate quantity used to simplify the computer computation. AL iscomputed from:

l AL=L-TS-S-DB The quantity AL, in effect, is the total length betweenthe forward edge of the main crosshead 20 and the end of the tool stack34 minus the length of the tool stack, the length of stem 24, and thedummy block length DB. The length of the tool stack must be taken intoaccount since it may vary, depending upon the die used. This, in effect,constitutes the total travel of the stem 24 during a complete extrusioncycle, disregarding the discard length D. In order to calculate thetotal travel of the stem 24, the quantity D, constituting the discardlength, must be subtracted from the quantity AL in digital subtracter 60to determine the quantity LS7, which is the total length of travel ofstem 24 during a complete extrusion cycle. The digital signalproportional to LS7 is then compared in comparator 62 with the output ofan up-down counter 63 connected to pulse generator 51; and when the twoare the same, comparator 62 actuates a pump control unit 64 to reducethe output of pump 44 to zero, whereupon the advance of the crosshead 20and stem 24 will also stop.

The quantity LS7 is also used in digital subtracter 68 to cal culate thequantity LS7A, the slowdown distance from extrude speed in accordancewith the equation:

(2) LS 7A=LS 7-SDES The quantity SDES, of course, is the slowdowndistance from extrude speed. The quantity LS7A as determined insubtracter 68 is then compared with the output of up-down counter 63 incomparator 70, the output of the comparator being used to actuate thepump control unit 64 to reduce the volumetric output of pump 44 and slowdown the stem 24 just before the extrusion process is completed.

The quantity AL is further used in subtracter 72 to determine thequantity CP which is the point of contact between the stem 24 and thedummy block 40 during an extrusion cycle. This is calculated inaccordance with the equation:

(3) CP=AL-B where B is the length of billet 38. The quantity CP, inturn, is utilized in subtracter 74 to calculate the quantity L812, theslowdown from fast advance, in accordance with the equation: (4)LSl2=CP-SDFA where SDFA is the slowdown distance from fast advance asentered by the operator. The quantity L812 is then compared incomparator 76 with the output of up-down counter 63; and when the twoare the same, the pump control unit 64 is actu ated to reduce thevolumetric output of pump 44 and slow down the stem 24 during the rapidadvance cycle.

In the operation of the system, the operator will enter the quantitiesL, TS, S, DB, B, D, SDFA and SDES. In some cases, the quantities TS, S,DB, SDFA and SDES will remain con stant from billet to billet. Theoperator, therefore, need only be concerned with the billet length B andthe discard length D. Once these are entered, the quantities LS7, LS7Aand L812 are computed by computer 56; and the operator initiates theextrusion cycle by control apparatus, not shown. When the extrusioncycle is thus initiated, the pump control unit 64 causes the pump 44 topressurize conduit 46 to open valve 50 and permit fluid from reservoir42 to flow into the left end of cylinder 12 as the rapid advancecylinders 14 and 16 advance the crosshead 20 and the stem 24 to theright. This process will continue until the count of counter 63 matchesthe output of subtracter 68, meaning that the stem 24 should slow downfrom fast advance. Consequently, the pump control unit 64 now reducesthe volumetric output of pump 44 such that the crosshead 20 and stem 24slow down just before the stem en gages the dummy block and forces thebillet against the die 32.

The stem 24 will now advance at a reduced speed against the dummy block40; and when the dummy block is engaged, the pressure in conduit 46 willrise, thereby causing the dumping valve 50 to disconnect the right endof cylinder 12 from reservoir 42 and connect it to the output of pump44. The dumping valve 50, for example, may be of the type shown inLombard US Pat. No. 2,751,076, issued June 19, 1956. The stem will nowmove to the right under extrusion pressure until the output ofsubtracter 68 matches the pulses counted by counter 63, whereuponcomparator will cause the pump control unit 64 to reduce the outputpressure of pump 44 and slow down the advance of stem 24. Finally, whenthe pulses counted by counter 63 match the quantity LS7 as calculated insubtracter 60, comparator 62 actuates the pump control unit 64 to stopthe pump 44, whereupon the extrusion process is completed. Thereafter,the discard length and dummy block are extracted from bore 30 asexplained above; and the operator reverses the flow of fluid throughpump 44 via unit 64; whereupon the cylinder 12 is connected back to thereservoir 42 while fluid in conduit 48, which is now pressurized, causesthe pistons 21 in cylinders 14 and 16 to withdraw the crosshead 20 andstem 24 back to their original starting positions. When the stem isfully retracted, limit switch LS is tripped to reset counter 63 to zeroin the event that it has not counted down to zero during the reversestroke.

The control action of the invention prevents damage to extrusion diesand at the same time insures that the quality of resulting extrusionswill be constant. At the same time, the yield is materially increasedsince the operator can determine with a higher degree of precision theminimum possible discard length Although the invention has been shown inconnection with a certain specific embodiment, it will be readilyapparent to those skilled in the art that various changes in form andarrangement of parts may be made to suit requirements without departingfrom the spirit and scope of the invention.

We claim as our invention:

1. In a control system for an extrusion press of the type wherein abillet is inserted into a billet container having a die at one endthereof and a stem is forced into the other end of said container toextrude the billet through the die; the combination of means includingcomputer apparatus for automatically slowing down the rapid advance ofsaid stem into said container just prior to the time that the billet isforced against said die, means including said computer apparatus forautomatically slowing down the speed of said stem during extrusion ofsaid billet just prior to the termination of extrusion when apredetermined discard length of said billet remains in the container,and means including said computer apparatus for stopping the advance ofsaid stem when the discard length of the billet equals saidpredetermined discard length.

2. The control system of claim 1 including a pulse generator operativelyconnected to said stem for producing a number of pulses proportional tothe travel of said stem from its fully retracted position, andcomparator means for comparing the pulses produced by said pulsegenerator with digital signals at the output of said computer apparatusfor controlling movement ofsaid stem.

3. The control system of claim 2 wherein pulses from said pulsegenerator are applied to an updown counter and the count stored in saidcounter is applied to said comparator means.

4. The control system of claim 2 wherein said stem is advanced by rapidadvance cylinders and a main pressure cylinder, and including pump meansfor supplying hydraulic fluid to said cylinders, motor means for drivingsaid pump means, and pump control means controlled by said comparatormeans.

5. The control system of claim 1 including an operators console andmeans whereby the manually enters into said computer apparatus digitalsignals proportional to the total length between the trailing end ofsaid stem in its fully retracted position and the end of a tool stack onthe side of said die opposite said billet container, the length of saidtool stack, the length of the stem, the length of said billet, thelength of a dummy block inserted into said billet container behind thebillet, the desired discard length of the billet, the desired slowdowndistance from fast advance and the desired slowdown distance fromextrude speed.

1. In a control system for an extrusion press of the type wherein abillet is inserted into a billet container having a die at one endthereof and a stem is forced into the other end of said container toextrude the billet through the die; the combination of means includingcomputer apparatus for automatically slowing down the rapid advance ofsaid stem into said container just prior to the time that the billet isforced against said die, means including said computer apparatus forautomatically slowing down the speed of said stem during extruSion ofsaid billet just prior to the termination of extrusion when apredetermined discard length of said billet remains in the container,and means including said computer apparatus for stopping the advance ofsaid stem when the discard length of the billet equals saidpredetermined discard length.
 2. The control system of claim 1 includinga pulse generator operatively connected to said stem for producing anumber of pulses proportional to the travel of said stem from its fullyretracted position, and comparator means for comparing the pulsesproduced by said pulse generator with digital signals at the output ofsaid computer apparatus for controlling movement of said stem.
 3. Thecontrol system of claim 2 wherein pulses from said pulse generator areapplied to an up-down counter and the count stored in said counter isapplied to said comparator means.
 4. The control system of claim 2wherein said stem is advanced by rapid advance cylinders and a mainpressure cylinder, and including pump means for supplying hydraulicfluid to said cylinders, motor means for driving said pump means, andpump control means controlled by said comparator means.
 5. The controlsystem of claim 1 including an operator''s console and means whereby themanually enters into said computer apparatus digital signalsproportional to the total length between the trailing end of said stemin its fully retracted position and the end of a tool stack on the sideof said die opposite said billet container, the length of said toolstack, the length of the stem, the length of said billet, the length ofa dummy block inserted into said billet container behind the billet, thedesired discard length of the billet, the desired slowdown distance fromfast advance and the desired slowdown distance from extrude speed.